Green Grotto Caves
2 miles east of Discovery Bay

At the bottom of the cave lies a subterranean lake where you can ride on a boat. The cave was used as a hiding place for many people throughout history, from pirates to the Spanish governor, who was looking for a place to avoid the British.

This is a good destination for those who want to see caves without really going off the beaten path. It's also a good choice for a rainy day activity; the 45-minute guided tour is along paths appropriate for everyone in the family. By US cave standards, admission price is fairly steep ($20) but this tour does give you a good alternative to the beach for a while.